from enum import Enum
from typing import Literal
from typing import Optional

from pydantic import BaseModel, Field, model_validator


class ChangeOp(str, Enum):
    CREATE = "create"
    UPDATE = "update"
    DELETE = "delete"


class PatchHunk(BaseModel):
    type: Literal["append_end", "replace_between", "replace_line_equals"]
    new_text: str = Field(default="")
    start_anchor: Optional[str] = None
    end_anchor: Optional[str] = None
    old_line: Optional[str] = None

    @model_validator(mode="after")
    def validate_hunk(self) -> "PatchHunk":
        if self.type == "append_end":
            if not self.new_text.strip():
                raise ValueError("append_end requires non-empty new_text")
            return self
        if self.type == "replace_between":
            if not (self.start_anchor and self.end_anchor):
                raise ValueError("replace_between requires start_anchor and end_anchor")
            return self
        if self.type == "replace_line_equals":
            if not self.old_line:
                raise ValueError("replace_line_equals requires old_line")
            if not self.new_text:
                raise ValueError("replace_line_equals requires new_text")
            return self
        return self


class ChangeItem(BaseModel):
    op: ChangeOp
    path: str = Field(min_length=1)
    base_hash: Optional[str] = None
    proposed_content: Optional[str] = None
    reason: str = Field(min_length=1, max_length=500)
    hunks: list[PatchHunk] = Field(default_factory=list)

    @model_validator(mode="after")
    def validate_op_fields(self) -> "ChangeItem":
        if self.op in (ChangeOp.UPDATE, ChangeOp.DELETE) and not self.base_hash:
            raise ValueError("base_hash is required for update/delete")
        if self.op in (ChangeOp.CREATE, ChangeOp.UPDATE) and self.proposed_content is None:
            raise ValueError("proposed_content is required for create/update")
        if self.op == ChangeOp.DELETE and self.proposed_content is not None:
            raise ValueError("proposed_content is forbidden for delete")
        return self


class ChangeSetPayload(BaseModel):
    schema_version: str
    task_id: str
    changeset: list[ChangeItem]